The present invention relates to desalination, and more particularly to a method of and apparatus for destination and fresh water recovery which does not require high temperature vaporization.
Conventional desalination techniques include vaporization of saltwater by heating, and subsequent condensation of the water vapor. These processes have very high thermal energy requirements; typically more than 2,000 joules per gram of water are required to vaporize the water. Therefore, in order to be economical, conventional desalination processes require that as much heat as possible be recovered during condensation of the water vapor. Complete heat recovery is impossible and even the best designed long vertical tube evaporators and flash distillation units require at least 30 joules per gram of water. This is far above a theoretical minimum value of less than two joules per gram of water for removing salt out of solution.
I order to eliminate the heat loss caused by imperfect heat recovery during the condensation stage of the conventional desalination techniques, it would be necessary to vaporize the saltwater without heating it. U.S. Pat. No. 4,323,424 issued Apr. 6, 1982 to Secunda et al. discloses a method and apparatus for generating a stream of high velocity saltwater droplets that vaporize without being heated. Salt precipitates from the vaporizing saltwater droplets, and the resultant water vapor can be recovered as fresh water.
According to the method disclosed in the patent, saltwater is atomized to create small saltwater droplets, no larger than six microns, that evaporate in relatively dry ambient air under standard conditions. Thus, the mechanism for evaporation is diffusion. Evaporation is complete and dry salt particles of the order of one micron are recovered. The water vapor is subsequently collected as fresh water.
One technique for atomizing the saltwater disclosed in the patent is the use of an atomization nozzle through which air and water flow under high pressure. The patent teaches an air to water mass flow ratio of about 17:1 and about 0:1. The high mass of air relative to the mass of water flowing through the atomizing nozzle limits the mass flow rate of the water and thus the volume of fresh water that can be collected.
Additionally, the patent disclosure is directed toward the recovery of the dissolved salt or other solute, and teaches the recovery of fresh water simply by placing a collection screen in the flow path of the water droplets There is no structure or technique disclosed for maximizing the amount of fresh water recovered.